The present invention relates to internal-combustion engines designed to operate selectively with gasoline and gas (for example, methane or LPG), of the type comprising a gasoline-supply system comprising a plurality of electronically controlled gasoline injectors, each of which is associated to one of the cylinders of the engine, a gas-supply system comprising a plurality of electronically controlled gas injectors, each of which is also associated to one of the cylinders of the engine, and electronic means for controlling the gasoline injectors and gas injectors.
The present applicant has already studied and proposed various solutions for internal-combustion engines of the type specified above (see, for example the European patent No. 0801223).
The purpose of the present invention is to provide a process for controlling an internal-combustion engine of the type specified above, which enables prevention of the drawbacks that occur with the engines so far built during the fuel-switching phase, i.e., during switching from gasoline supply to gas supply, or, vice versa, from gas supply to gasoline supply.
One first drawback that occurs during the said switching phase in engines according to the known art is represented by the considerable thermal stresses to which the catalytic converter provided in the engine-exhaust system is subjected on account of the undesired fluctuations in the metering of fuel during the phase of transition from one fuel to the other.
A further drawback that arises in known systems is represented by the possibility that inhomogeneities may occur in the delivery of the torque during the above-mentioned switching phase, with consequent problems from the standpoint of proper drivability of the vehicle.
The problems mentioned above derive from the fact that when the engine is switched from gasoline operation to gas operation, or vice versa, an initial transient phase occurs in which there is a joint presence of the two fuels in the cylinders of the engine. The simultaneous presence in the combustion chambers of the cylinders of the three components air, gasoline and gas gives rise to anomalies in the creation of the mixture. These problems are increased by the different state (liquid and gas) of the two fuels. In particular, in operation of the engine under normal running conditions with gasoline supply, a film of gasoline is deposited on the walls of the fuel supply pipes, the presence of which is important for proper operation of the engine. Vice versa, in operation of the engine with gas supply, proper filling of the combustion chamber is always guaranteed by the volatility of the fuel used. Switching from gasoline supply to gas supply, or vice versa from gas supply to gasoline supply, thus entails additional problems. The drawbacks that derive therefrom in the engines according to the known art are such as to force the adoption, in certain cases, of drastic solutions consisting in allowing the switching operation only when the vehicle is stationary, so as to prevent any possible problem from arising in driving on account of any loss of torque following upon fuel switching when the vehicle is travelling.